A body can be thought of as a group of systems working together to maintain a person's health. For example, the circulatory system can be responsible for providing oxygen and nutrients to various organs. The heart can be thought of as the central organ of the circulatory system. The left portions of the heart can draw oxygenated blood from the lungs and supply it to other parts of the body. The body can use the oxygenated blood as part of a metabolic cycle. The metabolic cycle can partially deoxygenate the blood while providing energy to organs or muscle tissue. The right portions of the heart can then return such deoxygenated blood to the lungs where the blood can become oxygenated again.
A variety of physiologic conditions can affect the mechanical or electrical behavior of the heart. A disease such as heart failure (“HF”) can reduce the pumping capability or efficiency of the heart. As congestive heart failure progresses, the reduced pumping capability or efficiency of the heart can cause other undesirable symptoms, such as edema (retention of body fluid), weight gain, shortness of breath, poor exercise tolerance, sleeping related problems, or other undesirable symptoms, and can ultimately lead to death.